This application claims the priority of German patent 198 33 079, filed Jul. 23, 1998.
The invention relates to a method for correcting a weft fault on weaving machines, especially air-jet weaving machines with pneumatic selvedge tucking devices disposed at the entry and exit ends of a shed, wherein a weft thread is blown by a main nozzle into the weft thread input channel of a reed and is recognized and detected by a weft thread monitor as a weft fault present at the exit end of the reed, wherein the end of the weft thread is held by a suction nozzle disposed at the exit end of the weft thread monitor, according to which the cutting of the weft thread between the main jet nozzle and the selvedge tucking device at the entry end is prevented, wherein the weft thread is beaten by the reed against the edge of a fabric and bound in by warp threads, wherein the previously performed tying in of the weft thread is undone, according to which the weft thread is released from the edge of the fabric with formation of a weft thread loop and drawn out of the shed by the suction of the suction nozzle.
The invention further relates to a weaving machine with at least two head frames forming a shed, with a main jet nozzle, with a plurality of relay jets, with a reed beating the weft threads against the edge of a fabric, with a weft thread injection channel, with at least one weft thread monitor present at the exit end of the weft thread injection channel, with a stationary suction nozzle disposed at the exit end of the weft thread monitor, with a pneumatic selvedge tucking device at the entry end and with a pneumatic selvedge tucking device at the exit end, and with an entry-end and an exit-end weft thread shear.
Weaving machines, especially air-jet weaving machines, are known, which are equipped with purely air-driven selvedge tucking devices for the formation of tight, closed fabric edges.
One selvedge tucking device is positioned on the entry side and one on the exit side of a shed to be formed and close to the outside edge of a fabric in the weaving machine, such that the weft thread injected into the shed, when it is beaten to the leading edge of the fabric by a reed, arrives simultaneously over the approximately V-shaped weft thread inlet of the selvedge tucking device into an end-limited centering slot of the selvedge tucking device lying approximately in the plane of the leading edge of the fabric.
After a weft thread correctly placed into the shed has been beaten onto the edge it is cut by weft thread shears disposed as is known in the particular selvedge tucking device and then the weft thread ends are pneumatically returned into the shed which as a rule follows the shed whose weft threads have bound off the previously injected weft threads.
If in the course of the weft thread insertion process a fault of any kind has been found and detected by control devices during the process of inserting the weft threads, a procedure known in itself is automatically started for remedying this error usually present in the weft thread. This procedure is known to those skilled in the art as "automatic weft break correction."
The procedure of automatic weft break correction assumes, among other things in air-jet weaving machines, that downstream and at the outlet end of the weft thread injection channel of a reed, means are present for seizing and pulling out the weft thread in question; that the weft thread involved, which has been beaten to the edge of the fabric is not being cut by the weft thread shears, and that so-called relay jets are present across the width of the weave which release the weft thread from the fabric edge with the formation of a so-called weft thread loop while the shed is open.
Together with this releasing action, the means for pulling out the weft thread is active, so that a programmed weft thread length can be drawn out to remove the weft fault from the pulling means, which is usually a pneumatically acting suction nozzle.
On account of the different geometrical circumstances necessarily present in an air-jet weaving machine, the position of the stationary air selvedge tucking device and the position of the fixedly arranged suction nozzle, the weft thread to be released from the cloth edge is pulled at an angle through the centering slot of the selvedge tucking device. In the case of looping the weft thread, the result of this is that the loop catches on the weft thread side of the centering slot, that is, it cannot be pulled away without the danger that the weft thread will hang up at the centering slot or break off.
The invention is addressed to the problem of finding measures to assist the automatic correction of a weft fault when fabrics are made with pneumatically produced edges.
The problem is solved according to the invention by adding a process step to the known procedure of automatic weft fault correction, which consists in the fact that at least one air pulse is applied to the weft thread to be released from the leading edge of the cloth, such that the loop in the weft thread lies outside of the centering slot of the selvedge tucking device when the weft thread is pulled out or at least it leaves the centering slot.
For the performance of the additional process step, an air-jet nozzle is provided according to the invention, whose outlet is aimed at a section of weft thread which is on the outlet side of the shed and which is preferably aimed at the weft thread in the centering slot of the selvedge tucking device.
It is an advantage when the air is tangent at least on the warp side of the centering slot of the selvedge tucking device and therefore strikes the weft thread inside of the centering slot. This means that the air jet issues from the nozzle at an acute angle to the longitudinal central axis of the selvedge tucking device.
In an embodiment of the invention provision is made such that the centering slot of the selvedge tucking device has over a certain length L on the warp thread side a target surface formed in the direction of the upper warp threads and one formed in the direction of the lower warp threads in order to achieve a sufficiently great effectiveness of the air blast in the centering slot and to assist the slipping of the weft thread out of the centering slot.
It is contemplated to provide another air nozzle alongside the first air nozzle present according to the invention, i.e., to provide it downstream from the centering slot, in order to assist the effectiveness of the looping of the weft thread out of the centering.
According to the invention, an additional flow channel can be present in the selvedge tucking device on the exit side, the outlet of which is aimed at the weft thread.
According to the invention it can furthermore be provided that the selvedge tucking device is positively steered out of the critical area of the weft thread movement or is swung by the pulling weft thread itself out of its working position and swung back to its working position after the end of the weft fault correction.
With the solution according to the invention, the automatic elimination of weft faults in the production of fabrics with insertion edges produced by pneumatic selvedge tucking devices can be executed without interrupting the progress of the work.
Manual intervention in the system by the operator is avoided and stoppage of the weaving machine resulting therefrom with its consequences, such as start-stop marks in the fabric, are reduced.
The solution according to the invention thus contributes to increasing the effectiveness of an air-jet weaving machine with pneumatic selvedge tucking devices.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.